A headless compound word whose meaning refers to the collective or sum of its component words, for example
bittersweet which, as an adjective, means both "bitter" and "sweet" simultaneously.
Most English dvandva compounds are hyphenated, as in Parent-Teacher Association, where "parent-teacher" is a dvandva compound referring to both parents and teachers together.
The word "dvandva" comes from Sanskrit grammar; "dvandva" means pair. Dvandva compounds are also called copulative.